The invention relates to a method for preparing O,O-dialkyl S-[2-(alkylthio)alkyl] phosphorodithioates. More particularly, the invention relates to a method of preparing O,O-dialkyl S-[2-(alkylthio)alkyl] phosphorodithioates by treating an O,O-dialkyl dithiophosphoric acid with a base in the substantial absence of organic solvent to obtain an O,O-dialkyl dithiophosphoric acid salt that is in turn treated with a thioalcohol derivative to form the O,O-dialkyl S-[2-(alkylthio)alkyl] phosphorodithioate.
O,O-dialkyl S-[2-(alkylthio)alkyl] phosphorodithioates, such as O,O-diethyl S-[2-(ethylthio)ethyl] phosphorodithioate, can be used as pesticides. The compounds are active against insect pests such as aphids, mites, leafhoppers, flea beetles, bean beetles, potato beetles, and thrips.
U.S. Pat. No. 2,759,010 discloses a process for preparing esters of dithiophosphoric acid by reacting O,O-dialkyl dithiophosphoric acids, either as alkali metal salts or in the presence of acid-binding agents, with a compound of the formula hal(CH2)x-S—CyH2y+1. U.S. Pat. No. 2,759,010 teaches the use of solvents such as benzene, ketone, and alcohols and exemplifies reacting O,O-diethyl dithiophosphoric acid with β-chloroethyl ethyl sulfide in the presence of benzene and pyridine.
U.S. Pat. No. 4,416,834 discloses a process for preparing compounds of the formula
by reacting a dialkyl thiophosphate salt with an ethylmercapto compound. U.S. Pat. No. 4,416,834 teaches that the dialkyl thiophosphate salt is prepared by reacting a dialkyl phosphite with sulfur in the presence of on organic solvent, such as toluene or xylene, followed by treatment with an aqueous base.
U.S. Pat. Nos. 4,283,335 and 4,283,338 teach processes for preparing O,O-dialkyl dithiophosphoric acid esters by reacting an O,O-dialkyl dithiophosphoric acid with an organic chloride that contains at least one acid-replaceable chlorine atom on a carbon atoms attached to oxygen, sulfur, or nitrogen by a single bonds, such as dichloro-p-dioxanes, in the presence of a catalytic amount of zinc chloride, ferrous chloride, or stannous chloride.
Because handling organic solvents may be difficult and/or costly, a need exists for methods of producing O,O-dialkyl S-[2-(alkylthio)alkyl] phosphorodithioates that do not require the use of organic solvents such as toluene or xylene.
Accordingly, it is an object of the present invention to obviate problems of the prior art. The present invention provides a method of producing O,O-dialkyl S-[2(alkylthio)alkyl] phosphorodithioates that does not require the use of organic solvents, such as toluene or xylene, and produces lower levels of by-products, thereby also providing advantageous environmental and economic benefits.